[SCSI] ipr: add writeq definition if needed

Compiling the driver will fail on 32 bit powerpc and other
architectures where writeq is not defined.  This patch adds a
definition for writeq.

Signed-off-by: Wayne Boyer <wayneb@linux.vnet.ibm.com>
Acked-by: Brian King <brking@linux.vnet.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>